Conversion of powdered polymers

ABSTRACT

Carbomer or cross-polyacrylate polymers which are conventionally provided in a powdered form are converted to a granulated, pelletized or tablet form for subsequent use, in combination with a liquid medium, to form a gel from which products such as liquid detergents, cosmetics and toiletries can be produced. Conversion of the polymer into a granular, pelletized or tablet form has been demonstrated to improve handling of the dry polymer, thereby mitigating against many of the problems incurred with the use of conventional powders, as well as to improve the rate of blending of the polymer with a liquid medium. In some embodiments, the polymer is blended with an electrolyte which may be a salt, acid or acid salt having a pK which is at least 1 unit, and preferably 2 units, greater than the pK of the polymer.

This application is a 371 of PCT/GB93/00965 filed May 10, 1993.

The present invention relates to carboxylic acid polymer compositionsand particularly relates to concentrates of acrylic acid polymers andtheir use to prepare gels of diluted and neutralized polymer.

The polymers to which the invention relates include cross-linkedpolymers of acrylic acids which are widely used as thickeners,stabilizers and emulsifiers in many industries. Said cross-linkedpolyacrylic acids are produced and sold under a number of trade namesfor example Carbopol (B F Goodrich), Acrisint (Sigma), Pemulen (B FGoodrich) Junlon (Nihon Kogakyu), etc. They are however most oftenreferred to by either of the generic terms carbomer orcross-polyacrylate, (developed by the Cosmetics, Toiletries andFragrances Association). The polymer products are referred to by thesenames in this application.

Said products so described are supplied in the form of very fine powderswith poor flow properties, and handling of these products is not easy.However, it has always been considered that the products must be in theform of very fine powder if complete wetting and reasonably rapidhydration of each particle is to take place when the products are addedto a liquid medium, such as water, to form a gel from which productssuch as liquid detergents, cosmetics, toiletries or pharmaceuticalproducts can be made. A consequence of the products being in the form ofa very fine powder is that they have a pronounced tendency to dust andfly about the work place even when care is taken to minimise this.

It is conventionally regarded therefore that, despite the handlingdifficulties, the products must be supplied in the form of fine powderssince, when they are to be converted to a gel, and in the initial stageof hydration for this conversion, i.e., wetting of the powders, theformation of a very stiff gel on the outside of the powder particlesoccurs which delays and restricts the entry of further water to hydratethe remainder of the particle. The stiff gel on the outside of theparticle therefore tends to prevent further water ingress into theparticle, thereby retarding the formation of a smooth gel. In addition,agglomerates of the powder particles form lumps which increases theproblem of wetting out and dispersion.

Furthermore, when disturbed, the dry powder tends to develop strongelectrostatic charges which impairs further the ability of the powder toflow in the required direction and, in the extreme, causes smallagglomerates to fly about which results in loss of material. This makesthe automatic measuring out of the carbomers virtually impossible.

As a result of these problems, manufacturers of the products alwaysadvise that the said product be carefully sifted into the water in anattempt to break up the dry agglomerates which tend to form duringstorage. Furthermore, these carbomers, when fully swollen and hydrated,have the property of suspending insoluble gases, liquids and solids.This property, although very desirable in most instances, can make theremoval of air bubbles from the mixture very difficult, if notimpossible, within a reasonable period of time.

In an attempt to overcome this problem it has been proposed to prepareconcentrated dispersions of resins in water. However, due to the highviscosity of said resins, they are extremely difficult or impossible tohandle. A further initiative, as described in co-pending application No9114095.4 provides, by incorporating small proportions of salts ofmulti-valent cations in these dispersions either by dry blending thepolymer and salt together before adding them to the water; or by mixingthe salt, carbomer, and water in any order, a concentrate which has beenfound to be extremely effective and to have gained acceptance as aworkable alternative.

The provision of said multi-valent cations in the blend has been foundto be acceptable but further research has shown that the importantfactor of handling difficulties of the powdered carbomer in a dry stateis not properly addressed. The addition of additional matter to thecarbomer, although having an important effect on the characteristics ofthe carbomer, does not solve many of the other inherent handlingproblems of the carbomer, and also meets resistance from users reluctantto change to a product which requires new certification and approval.For example, the form in which the carbomer is provided is important inallowing improvements both in the mixing of the carbomer in a liquidmedium to form the gel and also in improving the storage characteristicsof the carbomer.

The aim of the present invention therefore is to provide an improvementin the form in which a polymer is provided such that the ease of mixingor blending of the polymer in a liquid medium to form a gel is improvedin relation to existing powdered polymers and the polymer in itsimproved form is non-dusting, non-static and has improvedflow-characteristics.

The present invention provides for the conversion of a powdered polymerwherein said polymer is converted to a granular, pelletized or tabletform.

Typically said polymer will be a powdered carbomer or cross-polyacrylateand will, in a first embodiment be comprised wholly of carbomer, orcross-polyacrylate.

The carbomer in its converted form will be capable of rapid dispersionwhen added to a liquid medium to form a gel substance.

In a second embodiment, the polymer will comprise a carbomer orcross-polyacrylate with which is blended an electrolyte to form acomposition which is subsequently converted to a granular, pelletized,or tablet form.

Typically said electrolyte will have any of the followingcharacteristics, namely it is;

readily soluble in liquid,

an acid or salt or acid salt of mono-or poly-valent cations orcombinations thereof,

a salt, acid or acid salt, whose pK value is at least 0.5 units andpreferably 1.0 unit, less than the pK value of the carbomer itself whichis typically 4.3,

preferably solid and non-volatile at normal temperatures,

preferably non-toxic,

stable under normal storage conditions and preferably does notdiscolour, polymerize or change in any other way.

Typically, said electrolyte will also be non-hygroscopic.

When said electrolyte is an acid, or an acid salt, the pK value of theacid, a measure of its acidity, will, be at least equal to, andpreferably 1.0 unit less than the pK value of the carbomer.

Preferably, the pK value of the acid will be 2.0 units less than the pKvalue of the carbomer, which typically has a pK value of 4.3.

In a further aspect of the invention, the electrolyte used in a blendedform with the carbomer, will be an acid salt of mono-valent ormultivalent cations.

Typically said blend will be easily granulated or pelletized and will besupplied in that form. To form said pellets, tablets, or granules intothe required gel will require the conventional addition and mixing witha liquid medium followed by neutralisation of the mixture. Typicallysaid liquid medium will be water but may also be any of an organicsolvent such as ethanol, propylene glycol or a blend of a polarhydroxylic solvent and a non-swelling solvent.

Preferably, the polymer will be provided in a granular form. Typicallyto form granular products, either wet or dry granulation methods can beemployed. Dry granulation involves the use of high pressure to force theparticles into contact with each other and can be carried out either inmoulds by means of a ram or by forcing the powder through a screen withrollers. Subsequently the material may be reduced in size and putthrough screens to enable a selected size range to be obtained. Wetgranulation typically involves treatment with a small proportion ofwater to assist binding of the particles which then occurs without theneed for high pressures. Other solvents can be used, but in thisinstance would be considered undesirable. Drying of the granularmaterial may also be carried out as part of the process.

Conventionally it is generally held that for materials of the type ofthis invention, small particle size is essential if the rate ofhydration of the said materials is to be acceptably short; hence theprovision of the carbomer in powder form. This has, to date, preventedthe use of larger particle sizes as the rate of hydration has hithertobeen deemed to be too slow to be economically or practically possible.The provision of carbomer in granular, tablet or pellet form is ineffect contrary to the conventional wisdom as it increases the size ofthe carbomer parts to be mixed, but unexpectedly achieves significantimprovements.

The improvement of the mixing of the granules with the liquid medium ispossibly due to the reduction of air held in the mixture allowing thequicker addition of the granules and dispersion of same.

A further, decreased degree of swelling of the composition is shown, bythis invention, by optionally adding small proportions of electrolytewhen the polymer is in its acid form. It is shown that only a smallfraction of the amount of electrolyte required to reduce viscosity ofthe neutralized form of the polymers is needed to achieve the sameeffect in the acid form. The invention therefore provides a means ofadding said electrolytes to the said polymer when the polymer is in theacidic form prior to neutralization. The fraction of the electrolyterequired is so small that a reduction of viscosity of the neutralizedform is less than the experimental error in measuring same and hence canbe disregarded.

It has been found that the main advantages are in the handling of thepolymer and at the same time improving the mixing characteristic of thepolymer during hydration.

The original carbomer or cross-polyacrylate which is supplied in apowder form is necessarily of low bulk density, generally between 200and 250 kg per cubic meter wherein the granulated product of theinvention has a notably greater bulk density up to 600 kg per cubicmeter, hence providing considerable saving in terms of a reduced cost ofpackaging and storage.

A main advantage of the granulate or pellets of the invention is that bygranulating or pelletizing the mixture then the drawbacks of theoriginal powders previously discussed are overcome in that the granules,pellets or tablets of the invention are non-dusting and do not developstatic charges. A further advantage is that the granules flow veryreadily and disperse, even when rapidly added to stirred water, withoutthe disadvantage of clumping occuring. Furthermore, when required, theviscosity of the acidic gel can be reduced with the addition of theelectrolytes into the carbomer and subsequently granulating thecomposition and hence the requirement to remove any unhydrated materialby a stirring process is greatly reduced. Providing the said material inthe form of granules or pellets, either with or without electrolyteadditives, allows the materials to be used with automatic weighingsystems hence improving the efficiency of handling of the material incomparison to those products which are currently available.

Examples comparing the effect of granulating carbomers in relation tothe conventional powder are now discussed:

EXAMPLE 1

Carbopol 980 (BF Goodrich & Co Product) was compressed in a standardtablet press to give tablets with a diameter of 2.9 cm width and 0.8 cmdepth. The tablets were carefully crushed and sieved to remove any finesand over-size particles. The resulting granulate, with a particle sizebetween 0.2 and 0.6 mm flowed readily and evenly, did not clump togetheron shaking or stirring, and was free from a tendency to dust. On beingrapidly added to 100 times its own weight of stirred distilled water,the particles dispersed readily and became fully hydrated within 30-60minutes to give a translucent viscous mucilage which retained much ofthe air entrained within it during the mixing.

Comparison mixtures were prepared from the same batch of Carbopol 980using conventional techniques as follows:

a) by adding the powder carefully to the distilled water to avoidlumping as the powder came into contact with the water. Some dusting ofthe powder was noted. The time taken for the powder to hydrate fully wasagain between 30 and 60 minutes and a similar mucilage resulted as thatdescribed above.

b) the powder was added at the same rate as the granulate. More dustingwas observed and a number of large agglomerates were formed. These tookmany hours to fully wet out and hydrate. When the hydration was completethe mucilage was similar to that produced by method (a) above.

EXAMPLE 2

100 g of Carbomer 940 in a rotating plate granulator was sprayed withwater until agglomeration started. Approximately 6 ml was needed toreach this point, the process was continued until the particle size hadincreased to about 1 mm. The resulting granules were free-flowing andnon-dusting. When added rapidly to stirred demineralised water, theyrapidly dispersed and then hydrated within approximately 30 minutes togive a viscous translucent mucilage.

The examples given above clearly indicate that the granulation of thecarbomer allows the carbomer to be added to the water at faster flows,at a more economic flow rate whilst ensuring that a usable mucilage isobtained. This faster flow rate is achieved by the granulation of thecarbomer and the end result can only be equalled using conventionalcarbomers if the carbomer powder is added extremely slowly in an attemptto prevent lumping occuring. Attempts to add the powder at the same rateas the granules results in a substandard mucilage being produced.

Further advantages are obtained in that the dusting problem experiencedusing conventional techniques is eliminated by granulation and thehealth and safety problems associated therewith are eliminated.

Additionally, small levels of electrolytes may be added to improvefurther the mixing characteristic of the granules, pellets or tabletswith the liquid medium to form the gel and the following are examplesusing this process.

EXAMPLE 3

100 grams of Carbopol 940, a fine powder with a particle size range ofabout 1 to 5 microns, was placed in a rotating plate wet granulator andthe machine switched on. There was gradually added 10 ml of a 20% w/vsolution of magnesium sulphate heptahydrate by spraying. The liquid wasrapidly absorbed by the Carbopol and the mixture became granular withina short time, the granular product was then removed and passed through asieve having 12 mesh openings/linear inch. 2.5 grams of the materialwhich passed through the sieve was very rapidly added to a beakercontaining 500 ml of distilled water of room temperature while it wasbeing stirred. The granules immediately dispersed without lumpingtogether and over 30 minutes swelled to give a homogeneous low viscosityhazy solution which rapidly de-aerated when the stirrer was switchedoff. Sodium hydroxide solution was added to this solution until a stablepH value of 7.2 was reached. The viscosity, measured on a Brookfield RVTviscometer at 20 rpm, of the brilliantly clear bubble-free gel was 46000cps.

For comparison purposes a 0.5% solution of the same batch of Carbopol940 was made directly from the powder using the same technique. Thepowder was rapidly tipped into the water whereupon severe lumpingoccurred and these lumps took several hours to fully hydrate to give ahomogeneous mix. This solution did not allow the air entrained to riseout when stirring was stopped and when brought to a pH value of 7.2contained many bubbles although it was otherwise as clear as the samplemade from the granulated form. The viscosity measured in the same manneras before was 49000 cps

EXAMPLE 4

Similarly a sample of Carbopol 940 was dry blended with 2% of its weightof desiccated sodium sulphate; and dry granulated by compression. Thecoarse product was sieved to remove fines and particles larger than 10mesh, and the rejected material was returned for further working. Theresidual material was then tested.

    ______________________________________                 Viscosity cps                          Carbopol/sodium                 Carbopol only                          sulphate blend    ______________________________________    1% Carbopol 940                   960        3    un-neutralised    1% Carbopol 940                   57000      55000    neutralised pH 7.2    ______________________________________

The viscosity of the un-neutralised Carbopol was nearly the same aswater and since it did not exhibit any significant yield value the airwhich had been entrained in the solution rapidly rose to the surface sothat upon neutralisation the gel formed was completely free of airbubbles.

EXAMPLE 5

A further trial using 0.8% magnesium sulphate in place of the sodiumsulphate and the same batch of Carbopol 940 gave:

    ______________________________________    Viscosity un-neutralised cps                        4    Viscosity after neutralisation                        56000    ______________________________________

EXAMPLE 6

Blends of Carbopol 940 with 8% malic acid, and 0.6% sulphamic acid wereprepared and gave:

    ______________________________________                      0.67% sulphamic                                  8.0% malic            No addition                      acid        acid    ______________________________________    Viscosity 960         4           5    un-neutralised cps    Viscosity 57000       56000       40000    neutralised    ______________________________________

It is clear that the increased addition of malic acid needed to reachthe low un-neutralised viscosity has raised the overall electrolytelevel to a point where a marked loss of viscosity has occurred afterneutralisation, whereas there is virtually no loss of viscosity in thesample in which sulphamic acid was used. Because the malic acid, pK=3.4,is a much weaker acid than sulphanic acid (pK=1.92), much more is neededto effect the reduction in viscosity of the un-neutralised dispersion.

Other suitable acids include

Benzene-sulphonic acid

Citric acid

cyclo-propane-1,1-di-carboxylic acid

tartaric acid

however this listing is not intended to be exhaustive.

From these examples, it can be clearly seen that the addition of anelectrolyte to the carbomer, provides an acidic dispersion which has alower viscosity and hence can again be granulated, pelletised or formedinto tablets and supplied to the users in that form whilst maintainingan adequate rate of hydration comparable with the powders currentlyavailable. The addition of the said electrolyte to the carbomer in theacid form, as opposed to after neutralisation, is inventive and novel inits own right. The proportion of said electrolyte should not be so highas to seriously reduce the viscosity of the neutralised gel formed bydispersion of the granulate in water and adding sufficient alkali toreach the required pH value which will normally be in the range of5.0-8.5 but may for specific purposes be outside this range. It is alsoenvisaged that the controlled addition of acid over and above thatneeded to achieve the effect of reducing the viscosity of theun-neutralised dispersion can be used as a means of reducing the batchto batch variation of these polymers when neutralised and, furthermore,to bring said batches which have a viscosity above the specified limitinto specification. A further aspect of the invention therefore allowsthe manufacturer or user of the material to adjust and take into accountany variation which may occur in the un-neutralised dispersion whenhydrated.

It is known that the viscosity of carbomer dispersions in the acid formcan be reduced in viscosity by the addition of acid in small proportionand hydrochloric acid and phosphoric acid have been suggested. Blendingwith the carbomer before addition to the water is a novel concept andthe suggested acids would obviously be totally unsuitable in any case.Addition of electrolytes in the specific form of sodium salt of ethylenediamine-terra-acetic acid has also been recommended for controlling theviscosity of finished products by addition at the end of the process.

A specific embodiment of an industrial granulation technique to form thegranules of the invention is now described with reference to theaccompanying drawings wherein;

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a simplified partially schematic representation of anapparatus useful in the granule forming process.

Referring to FIG. 1, the apparatus comprises a carbomer supply means 2,a carbomer feed means 4, pressurised rollers 6, and two granulatingsieves 8 and 10.

The supply means 2 are provided to supply through gravity augmented by aspiral drive 12 carbomer powder into the feed means. The spiral drive isprovided to prevent bridging of the carbomer powder and to ensure thatthe powder will enter the feed means.

The feed means 4 comprises a plurality of powered augers 14 which act tomove the powder horizontally along cylinder 16 to the pressurisedrollers 6. As the powder passes through the rollers the powder iscompressed together into a flake 18 which subsequently breaks intosmaller fragments 20 as it enters the first granulating sieve 8.Provided adjacent each of the sieves is a rotating means with arms whichcause the flake to be forced through the first sieve 8 into the secondsieve 10 where the action is repeated and granules 22 of the requiredsize are deposited into a granule hopper (not shown). Typically the meshsize of the first sieve 8 will be larger than that of the second sieveto allow a staggered reduction in the granule dimension to the dimensionrequired.

Typically to form said granules, pellets or tablets into the requiredgel, will require the addition of a liquid form which will typically bewater but may also be an organic solvent such as ethanol, propyleneglycol or a blend of a polar hydroxylic solvent and a non-swellingsolvent.

It is generally held that carbomers of the type so described haveinherent problems in that static charges develop and dusting occurs whensaid carbomers are provided in powder form. These problems have beenaccepted by the industry as being unavoidable due to the need to usecarbomer in the powder from. This need has been based on the belief thatsmall particle size of the carbomer is essential in order to obtain aneconomical rate of hydration. Particles of greater size, it has beenbelieved, or the loose agglomerates formed on storage and byinter-particle attraction lead to a rate of hydration which is deemed tobe too long to be economically or practically possible. The inventionshows that this belief is incorrect.

The current invention, by providing the carbomer in a granulate, pelletor tablet condition eliminates the dusting problem and greatly reducesthe static charge development between particles yet has been found alsoimprove the rate of hydration or mixing characteristic of the polymer.These advantages are considerable in that handling of the carbomer andall the associated problems therewith is greatly improved whilst at thesame time the dispersion of the carbomer when forming into a gel is notadversely affected. This is in complete contrast to the currentlyconventional belief.

We claim:
 1. A powdered carbomer or cross-polyacrylate polymer of thetype used to form a gel when added to a liquid medium and neutralisedwherein said powdered carbomer or cross-polyacrylate polymer is blendedwith an electrolyte to form a composition which is converted to agranular, pelletised or tablet form.
 2. A polymer as in claim 1 whereinsaid electrolyte is soluble in water and is solid, non-volatile, andstable under normal temperature and storage conditions.
 3. A polymer asin claim 1 wherein said electrolyte is in the form of a salt, acid, acidsalt, or a combination thereof.
 4. A polymer as in claim 3 wherein theelectrolyte is a salt or an acid salt and the pK value of theelectrolyte is at least 0.5 units less than the pK value of the carbomeror cross-polyacrylate in the blend.
 5. A polymer as in claim 4 whereinthe pK value of the electrolyte is equal to or greater than 1.0 unitless than the pK value of the carbomer or cross-polyacrylate.
 6. Apolymer as in claim 3 wherein said electrolyte is an acid salt, the acidsalt being a mono- or polyvalent cation.
 7. A polymer as in claim 3wherein said electrolyte is an acid and has a pK value of at least 1.0unit less than the pK value of the carbomer or cross-polyacrylate in theblend.
 8. A polymer as in claim 7 wherein said electrolyte has a pKvalue of 2.0 units less than the pK value of the carbomer.
 9. Thepolymer as in claim 1 wherein the composition is converted to a granularform.